Numerous approaches have been developed to protect flammable substrates from fire. One approach that has found widespread utility is the application of fire-retardant coatings to the substrate. Fire-protective coatings may be broadly classified as ceramic-based coatings, ablative coatings, intumescent coatings, and vapor-producing (sublimation) coatings, although in practice there may be substantial overlap of the chemical and physical fire-retarding mechanism between these approaches.
Many conventional fire-retardant coatings employ agents which release non-flammable gases in response to heat or flame. For example, halogenated fire-retardants release gaseous acids, such as hydrobromic or hydrochloric acid, which retard burning by scavenging oxygen radicals. However, environmental and health concerns over halogenated flame retardant chemicals, such as brominated organic polymers, has led to an renewed emphasis on inorganic flame-retardants.
Alumina trihydrate (“ATH”) is an inorganic flame retardant defined by the chemical formula Al2O3.3H2O. In the presence of heat from fire, ATH endothermically releases its water of hydration which comprises 35% of the molecular weight of ATH. The endothermic reaction helps to cool the substrate below its flash point. The liberated water also provides a vapor barrier which shields the substrate from oxygen needed for combustion.
There are certain drawbacks to conventional coatings containing ATH and other inorganic fire-retardants. For example, due to the high levels of inorganic fire-retardant required to impart acceptable fire-retardancy, the coatings are typically rigid and therefore not suitable for application to highly flexible substrates. Cracking and checking of the coating frequently results when the underlying substrate is deformed, thereby diminishing the protective ability of the coating, exposing the substrate to the elements, and detracting from the visual appearance of the article.
Accordingly, there is a need in the art for highly flexible fire-retardant coatings. Further, there is a need in the art for highly flexible fire-retardant coatings comprising inorganic fire-retardants in quantities sufficient to retard or resist combustion of a substrate. There is also a need in the art for highly flexible fire-retardant coatings comprising inorganic fire-retardants in quantities sufficient to retard or resist combustion of a substrate which further protect the substrate or under-coating from water damage and the like.